Recently, I.sup.2 L (Integrated Injection Logic) circuits, which are known as a kind of digital circuit, have been employed in an analog IC in order to achieve higher integration and advanced functions in the analog IC since I.sup.2 L circuits are suited for coexisting with individual analog circuits. In this case, the analog IC including some I.sup.2 L circuits is typically designed so that it receives direct currents from at least two different power sources for respectively being supplied to the I.sup.2 L circuits and the remaining analog circuits in order to prevent electrical interference between these two types of circuit and/or to supply different voltages to these respective types of circuit.
In the case where the analog IC has at least two routes for respectively supplying direct currents received from different power sources, the analog IC can be set in a waiting state, for example, when the first power supply is in an off-state but the second power supply is in an on-state. In a bus-line interface of an IC for instance, during the waiting state, the I.sup.2 L circuits receive direct currents by the second power supply, while the remaining analog circuits do not receive direct currents due to the off-state of the first power supply. By this process, before the analog circuits are activated, bus-data can be set into the Analog IC and held in some of the I.sup.2 L circuits, or bus-lines at the output interface of the analog IC may be supplied with data held in the activated I.sup.2 L circuits.
However, in the conventional analog IC which includes a plurality of I.sup.2 L circuits, all the I.sup.2 L circuits receive currents, and in spite of some of the I.sup.2 L circuits being unused, these I.sup.2 L circuits are activated. For this reason, the greater the number of unused I.sup.2 L circuits, the more idle current is wasted. As a result, such analog IC gets to have a high electricity consumption.